1. Field of the Invention
The present general inventive concept relates to a developing unit which supplies a toner to an electrophotographic image forming apparatus to develop an image and an image forming apparatus using the same, and more particularly, to a developing unit where a blade is installed in different positions according to whether the developing unit is mounted to an image forming apparatus, and an image forming apparatus using the same.
2. Description of the Related Art
An electrophotographic image forming apparatus includes a developing unit which supplies a toner to an electrostatic latent image formed in a photosensitive medium to develop an image.
FIG. 1 is a schematic perspective view of a main body in a conventional developing unit. Referring to FIG. 1, the conventional developing unit includes a developing member 10 and a blade 20. The developing member 10 is installed to be in or out of contact with a photosensitive drum 30 and adheres a toner thereon to supply it to the photosensitive drum 30. The blade 20 regulates a height of the toner layer adhered on a surface of the developing member 10 to be a thin layer by pressing the surface of the developing member 10 at a constant pressure. Thus, the toner adhered on the surface of the developing member 10 becomes a thin layer by the blade 20 and is provided to the photosensitive drum 30, thereby developing an electrostatic latent image formed in the photosensitive drum 30.
The blade 20 includes a bending part 21 which is formed by a bending process and is made of an elastic metal plate. The blade 20 contacts the developing member 10 at a fixed position at a constant pressure to regulate a thickness of the toner layer.
The developing member 10 is generally provided as a conductive rubber roller which includes a compound of a nitrile butadiene rubber (NBR) based synthetic rubber and Epichiorohydrin Copolymer (ECO) or a silicon based rubber. Further, the conventional developing unit uses single component toner made of polyester resin to which a wax, a coloring agent, and a charge control agent are added therein and which is coated with silica and metal oxide thereon.
The developing unit with the aforementioned configuration is distributed with the toner being thereinside before installed on the image forming apparatus to be used. Here, the toner is positioned in the bending part 21 between the blade 20 and the developing member 10, and the developing member 10 is at a standstill. Thus, the coating agent of the toner is partially separated by the pressure of the free end portion of the blade 20 and adhered to the bending part 21 and the developing member 10 which is in contact with the bending part 21.
When an image is formed by the developing unit, a streak and a migration are generated.
The streak is generated by the coating agent adhered to the bending part 21 and formed on a printing medium in a proceeding direction of the printing medium when forming an image. The migration is generated by the coating agent adhered on the developing member 10 and formed on the printing medium in a parallel direction with the proceeding direction of the printing member in a period of rotation of the developing member 10.
In the conventional developing unit, the free-end portion of the blade 20 is fixed in a developing frame and contacts the developing member 10 at a high pressure, thus generating a significant amount of stress on the blade 20, the bending part 21 of the blade 20, and the developing member 10. During operation, the developing member 10 is rotated, thus no one area of the developing member 10 is subject to the stress for an excessive amount of time. Accordingly, a surface of the developing member 10, which is in contact with the blade 20 and the bending part 21 of the blade 20, may be deformed between operations while the developing member 10 is not being rotated.